NAVLE Hemic and lymphic

Canine Immune-Mediated Diseases Study Guide

Immune-mediated diseases of the hemic and lymphatic system represent a significant category of autoimmune disorders frequently encountered in canine practice.

Overview and Clinical Importance

Immune-mediated diseases of the hemic and lymphatic system represent a significant category of autoimmune disorders frequently encountered in canine practice. These conditions occur when the immune system erroneously targets normal blood components for destruction. The most clinically important immune-mediated hematologic diseases in dogs include Immune-Mediated Hemolytic Anemia (IMHA), Immune-Mediated Thrombocytopenia (ITP), and Evans Syndrome (the concurrent presentation of both conditions). These diseases carry significant morbidity and mortality, with IMHA mortality rates historically ranging from 30-70% despite aggressive therapy.

Type Description and Characteristics
Primary (Idiopathic) No identifiable underlying cause; approximately 60-75% of canine IMHA cases May have genetic predisposition; true autoimmune disorder
Secondary (Associative) Triggered by underlying condition, drug, or infection Common triggers: Babesia spp., neoplasia, drugs (sulfonamides, NSAIDs), vaccines

Immune-Mediated Hemolytic Anemia (IMHA)

Definition and Classification

IMHA is an autoimmune disease characterized by premature destruction of red blood cells (RBCs) due to antibody-mediated mechanisms. It is the most common autoimmune disease in dogs and represents a classic example of a Type II (cytotoxic) hypersensitivity reaction.

Pathophysiology

In IMHA, antibodies (primarily IgG or IgM) bind to antigens on the RBC surface, leading to cell destruction through two primary mechanisms:

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